This invention relates generally to a gas mask filter and method of using same or remove low levels of ethylene oxide from ethylene oxide contaminated air. The filter comprises dried ion exchange resin. At anticipated conditions of gas mask/face mask use, upon contact of ethylene oxide therewith, the resin catalyzes polymerization of the ethylene oxide at a rapid rate. Resulting polymer reaction products are tenaciously retained on the resin surface.
The wearing of protective face masks to filter out noxious gases has been a common industrial practice for a long time. For this purpose, filters comprising a wide range of absorbents/adsorbents and a variety of alternative structures have been used. To date, the only gas masks commercially available for general personnel protection from ethylene oxide inhalation have been based upon activated carbon media, often chemically treated (e.g., Mine Safety Appliances, Model GMEO-SSW).
Removal of ethylene oxide from air is industrially important to maintain environmental quality and to protect workers' health. Various designs for scrubbers are commercially available, all working on the same principle: The gas mixture, containing traces of ethylene oxide, is contacted with water. The water contains a dissolved catalyst, typically a strong acid such as sulfuric acid, or a strong base. This catalyst promotes the reaction of ethylene oxide with water (hydrolysis) to form ethylene glycol, which is a relatively innocuous and non-volatile compound. This scrubbing liquor is reused until the process efficiency decreases beyong an acceptable limit, due to the accumulation of ethylene glycol; at this point, the pH of the liquor must be adjusted (neutralized) before disposal.
While acid scrubbers perform adequately for process streams with moderate levels of ethylene oxide in air, reduction of ethylene oxide concentrations below a few parts-per-million is generally impractical. Likewise, room air cleaning, which involves larger air volumes and lower concentrations of ethylene oxide, cannot be performed with wet scrubbing unless prohibitively large water flow rates and huge equipment are employed.
The other systems currently available for ethylene oxide removal are based upon adsorption on activated carbon. Activated carbons have much lower capacity for ethylene oxide retention, when compared to the ion exchange resins described herein. Smaller device sizes can therefore be envisioned. Moreover, because ethylene oxide is retained on activated charcoal by comparatively weak retention forces of absorbtion, desorption may occur and the effectiveness of removal can vary unacceptably over time and under various conditions.
Ethylene oxide contaminant removal, at high levels, such as found in sterilizer effluents using exchange resins, is taught in U.S. Pat. No. 3,851,043, which discloses a system and method for the removal of ethylene oxide contaminants using gel-type ion exchange resins. In accordance with the method of U.S. Pat. No. 3,851,043, the presence of water is required. water is present in such an amount that ethylene oxide is reacted with the resin at a liquid solid interface; that is the reaction is effected in a liquid phase.
Ion exchange resins have also been used in methods of 1,4-Dioxane synthesis (See e.g. U.S. Pat. No. 4,355,071 and German Pat. No. 2,430,355) wherein an ethylene oxide stream is reacted with the resin to form an intermediate product. In such processes, once again, the intermediate reaction involving the resin and ethylene oxide is effected in liquid phase.
Specifically, acidic sulfonated polystyrene resins have been used in the prior art to catalyze the formation of a liquid ethylene oxide product (ethylene glycol and polyglycol liquids) in the presence of water in order to quantitatively measure ethylene oxide exposure. (U.S. Pat. No. 4,423,005)
The art also teaches the use of ion exchange resins as catalysts in the high temperature gas-phase reactions of ethylene-oxide to form ethylene glycol.
The present invention is based on the discovery that low level ethylene oxide contaminants can be removed from air by use of a filter comprising dried acidic ion exchange resins. The resin in the filter contains less than about 20% by wt. water. Reaction of ethylene oxide upon contact with the resin occurs substantially at a gas-solid reaction interface. Solid ethylene oxide polymer is rapidly formed and bound to the resin. The strength of the forces of attraction between polymer and resin are of such magnitude that retention continues after the ethylene oxide has been removed from the air, and during the period after contaminant removal when uncontaminated air continues to be passed through the resin. In accordance with this invention, permanent retention of polymer persists at conditions of use. Detrimental ethylene oxide-containing gaseous components are not "washed-out" of the resin during continuous use of the gas mask when ethylene oxide-free air passes through the mask.
It is notable that, in contrast to U.S. Pat. No. 4,423,005, this invention enlists ion exchange resins in systems where ethylene oxide and water concentrations are must more dilute than those encountered in sterilizer operations. In this regime, reaction products are formed which are largely bound to the resin, and water behaves as a rate inhibitor.
Much of the prior art described above depends upon ion exchange resins to catalize reactions of ethylene oxide. In the present invention, ion exchange resins are employed, to a large extent, as solid phase reactants.